Gerhard bad-mouths almost every ethnicity on the train... except for the French. Because even undercover, he can't bring himself to talk badly about the ethnicity of his late girlfriend.
Many of the characters purposely have "fights" in front of Poirot to drive him off from realizing they are allied.
The beginning of the movie mirrors the story. A guilty party (the police chief/Ratchett) hires (or tries to hire) Poirot, thinking he won't figure out their secret, yet he does.
The song in the first trailer ("Believer") becomes fitting when you consider how Cassetti put so many people through "PAIN"!
When refusing to protect Ratchett, Poirot makes a point that he got himself in trouble for getting mixed up with the wrong people. He's not too far off the mark. But ironically, the kind of people Ratchett's in trouble with aren't gangsters. On the contrary, he himself is a gangster, and the people he's in trouble with all happen to be non-gangsters. It also becomes ironic because Poirot tells Ratchett he hunts down criminals; he doesn't protect them, but by the end, he's been convinced to lie to protect a whole trainful of criminals.
Princess Dragomiroff mentions that Linda Arden would've turned to directing if not for the tragedy, and that she would've been a titan of Broadway. Seems a bit of a stretch for a great actress to be a great director, especially in the time the film is set...and then you learn that Linda Arden had been 'directing' everyone involved in the murder, utilizing several of their talents to her advantage and putting on a very convincing show for Ratchett and Poirot. She certainly had a talent for directing, and the Princess could tell.
When Poirot gives the passengers the opportunity to shoot him, he says Bouc can lie to the police but he can't. At the end of the story, it is Bouc who gives Poirot's other, flawed theory to the police while Poirot remains silent.
Poirot sighing over his Lost Lenore may seem Narmish, but it actually makes him more sympathetic towards the killers over theirLost Lenores.
When Poirot delivers The Summation to the passengers, everyone is seated in a row... almost like jurors listening to a lawyer arguing a case. It simultaneously reflects the original novel's establishing of the passengers as being a jury delivering a sentence on Casetti, and inverts it — instead of the 'jury' delivering its verdict on Poirot, Poirot is put into the position of delivering his verdict on what they've done and what he should subsequently do with them.
The suspects are also seated as a visual reference to Leonardo da Vinci's The Last Supper, except there's 12 of them. Poirot, their judge, could be considered the missing Jesus. If so, Linda Arden is sitting in Judas' position. Part of her despairing rant even notes that she considers the rest of the passengers good people who she inspired to do a bad act. Judas also realizes what he just did to Jesus and hanged himself; Linda Arden realizes the lengths she went through to get revenge and attempted to shoot herself.
The Secret Test of Character is how Poirot resolved his To Be Lawful or Good dilemma. Had someone attempted to shoot him, he'd have turned them in. Not only does no one try to kill him, they all cry "No!" when Linda Arden picks up the gun, showing that they are all unwilling to let someone else commit a murder to save them. Arden's attempted suicide proves that she understands the depths of their crime. All of this shows Poirot that they are still good people, whose moral sense had not been compromised.
This also explains why they didn’t kill Poirot after killing Ratchett to prevent him from solving what happened, they were unwilling to cross the line of killing an innocent bystander despite the real risk that he could figure out what happened and have them arrested.
When the train is delayed, everyone's complaining about the inconvenience and how their plans and connections are going to be delayed or outright destroyed, until Pilar delivers a rather intense speech about how their fate is in the hands of God and how they are not necessarily entitled to reach their destination on time. Everyone looks a bit uncomfortable. At the time, you might just pass it off as everyone feeling a bit unsettled by how deeply into God Pilar seems, but after The Reveal it becomes a lot more likely that they're all confronting what they've done, the possibility that their actions were not as justifiable as they might want to think and that they're not necessarily entitled to get away with it, and that they'll have to answer for it in some way.
Why does everyone seem so suspicious of everyone else? It's not because they think one of them's a murderer. It's because they think one of them might crack and expose what they've all done to Poirot. This explains why they all stare suspiciously at MacQueen when he comes back from his first interview with Poirot. They're worried that he might be the weak link.
Why's Poirot so concerned about his eggs being symmetrical in the first scene that he sends out for some more? It's part of his OCD, yes, but it's also because he's secretly arranged for the police inspector's office to be searched and is keeping him distracted from going back there.
MacQueen is shocked and dismayed Poirot is bunking with him because the 13th passenger, "Mr Harris," is fictional. The conspirators faked the reservation so that there would no passengers on the train who were not in on the scheme and might interfere. MacQueen was never supposed to have a bunkmate.
It also explains why Michel relocated MacQueen to a different room from Poirot: he wanted to make sure he was bunked with someone who was in on the plan.
The Count's introductory Establishing Character Moment where he beats up a paparazzo can be seen in a different light after rewatching: considering what he and his wife are about to be involved in soon, perhaps it also a case of nerves rather than just bad temper. Also, it might have been risky to have tabloids with photographic evidence placing them on the train at the same time as a murder - while it might not lead everyone to immediately think they were involved, it could still jeopardise the plan.
Poirot steps in camel excrement in the beginning of the film. While most people would realize it was disgusting, Poirot only notices how things are out of balance and steps in the poop with his other foot and is satisfied despite both of his shoes being dirtied and ruined. At the end of the film, Poirot does the reverse: he steps into a situation that is out of balance with a crime committed, but is forced to notice how messy and uncomfortable the situation is and ends with choosing a solution that cleans up the situation instead of restoring balance.
Poirot is upset by the lack of balance at the solution of the case: people committed murder by revenge and a definite crime, but Casetti was bad enough the passenger's morals are still higher. He also hates having to live with himself at letting the murderers go. But a balance is still in place in a way: both sides have to live with a decision that will torment them and both have thus received punishment for their actions.
When his identity is revealed, Hardman makes a point of apologizing to Poirot and his fellow investigators for the bigoted comments about race he made in his undercover identity, even though the person he made them towards and regarding — Dr. Arbuthnot — is not present. Of course, since Arbuthnot actually knows and is working with Hardman, Arbuthnot is probably well aware that Hardman was just acting and is not actually a racist, and so no apology to him is likely needed. The apology is to maintain his cover of not knowing Arbuthnot.
Second time watching this, one notices Helena is not among the people who stabbed Casetti. When you think about it, this is understandable on three levels. First, it's established that poor Helena is afraid of Casetti, afraid of how he indirectly killed her sister Sonya. She's too frightened to face the man who keeps her up at night. Second, Count Andrenyi (who seemingly has no direct attachment to the Armstrongs other than their relationship to his wife) possibly came along because, given his protectiveness of Helena, he meant to stab Casetti on her behalf. Thirdly, even if she couldn't stab Casetti, she still played a role in the conspiracy with the kimono Hardman lent her.(In the book, it's explained that Helena never left her cabin, and her husband took her place.)
McQueen is revealed to have been stealing money from Ratchett for years since he has been employed by the man. Given how many people are involved in this conspiracy to kill him, it seems likely not all have the financial means to get to Istanbul for the trip. McQueen likely helped with some of them by using Ratchett's own money to help pay for their travel rather than having one of the richer conspirators pay for things.
On first viewing Ms. Hubbard's following after Poirot as he boards the train can be seen as her flirting with him and being a bit drunk. On the second viewing, knowing she is really Linda Arden and the mastermind of the murder, the scene is now her trying to figure out who the new arrival she didn't plan for is.
As Poirot moves through the train station and later the train several of the characters talk with him or watch him walk by, such as Mary asking if he is traveling with them. It is only on repeat viewings one realizes they too are startled by the sudden arrival. That is why they suddenly begin talking with each other in private as the train leaves.
Bouc's concern for the black Dr. Arbuthnot becomes this after Death on the Nile reveals that he later fell in love with an black woman.
Given the implication that Cassetti/Ratchett made enemies with his business decisions everywhere he went; that his name was immensely infamous to the point that he changed it and that MacQueen has felt haunted about working for him for as long as he has and seeing all the terrible things that he has, would it be appropriate to believe that much like in both the book and other versions that Daisy Armstrong is not the first kidnapping victim he's had where he's basically done the exact same motif numerous times: ransom the victim for months; let others take the blame; kill the victim once he's done bleeding their family dry and then leave them all in complete shambles?
What happened to the captain who stole the priceless relic and tried to frame three holy men after the mob got him? Given that three groups of people were on the verge of a riot because of the accusations against their religious leader, and Poirot pointed out that the captain set them up to fall for his crime, they may have killed him if the guards couldn’t rescue him in time.
There are still plenty of police officers present; they almost certainly dragged the mob off him and arrested him.
Is MacQueen's father still alive after his ordeal with the Armstrong case, or did he kill himself out of shame? Either way, the answer is poignantly unsettling.
Linda Arden attempted suicide in front of her daughter. Imagine how horrific that was for the already-traumatised Helena, and how much more horrific it would have been ifthe gun hadn't been unloaded.
More horrific, it would've been yet another death ultimately attributable to Daisy's murderer. Even dead, Cassetti's plague on the Armstrong family persists...
Helena is in for a long period of withdrawal and insomnia after quitting her barbitol cold turkey.
Pilar claims she's a light sleeper. As proven in the flashback, the reason she became a light sleeper is that the last time she dozed off and didn't wake, Daisy, who was her charge, got kidnapped and the rest is history.
Another reading of the Count's assault on a paparazzo: his wife lost her niece, sister, unborn nephling, and brother-in-law due to fame. Daisy was only targeted because Captain Armstrong was so often in the papers. He has a very good reason to hate reporters.
